Most foundry castings use molds made from a sand and binder system. The binder allows the sand particles to adhere to one another so that the molds can be shaped. Green sand molds, which include a mixture of sand, clay, water, and coal dust, are commonly used in foundries. For complicated castings, cores can provide any necessary void spaces in the castings. Common core-making processes include shell, oil-baked, and no-bake.
After the molds are assembled, they are filled with molten metal. The methods for pouring molds vary greatly with the size and type of foundry. Following the mold-pouring process, the castings are allowed to cool. The castings are then removed from the molds in a process called "shakeout". Similar to the pouring operation, the shakeout operations vary greatly with the type of foundry. After shakeout, the casting may be placed in a blast machine to remove most of sand adhering to the new casting. However, some sand will be embedded or burned into the casting.
To remove the burn-in sand, the castings are cleaned by hand using pneumatic chipping and grinding tools. The grinding and chipping of the sand produces respirable silica particles, which may present a health hazard to workers if not adequately controlled. The workers use a variety of tools, including cup grinders, cone grinders, pneumatic chisels, and abrasive wheels. Engineering controls for this preparation is not universally used; many plants have no controls in place, while others may have ineffective controls, such as poorly designed ventilated tables. The National Institute for Occupational Health and Safety (NIOSH) in conjunction with the Mine Safety and Health Administration (MSHA) has approved the use of air purifying respirators with helmets, which have high efficiency particulate air (HEFA) filters and built-in face shields.
Silica may be present in at least three crystalline forms (alpha quartz, cristobalite, and tridymite), as well as amorphous (noncrystalline) forms. Amorphous silica is usually considered to be of low toxicity and may produce X-ray changes in the lung without disability. The crystalline forms of silica can cause severe lung damage (silicosis) when inhaled. Silicosis is a form of pulmonary fibrosis caused by the deposition of fine particles of crystalline silica in the lower portions (alveoli) of the lungs. Symptoms such as coughing, shortness of breath, chest pain, weakness, wheezing, and nonspecific chest illness, usually develop insidiously. Silicosis usually occurs after years of exposure, but may appear in a shorter time if exposures are very high.
The current U.S. Department of Labor, Occupational Safety and Health Administration (OSHA) Permissible Exposure Limits (PEL) for respirable crystalline silica is calculated from Equation 1: ##EQU1##
In 1989, OSHA changed the PEL to 100 .mu.g/m.sup.3 under the Air Contaminants Standard. In July 1992, the 11th Circuit Court of Appeals vacated this standard. OSHA is currently enforcing the limit calculated by Equation 1; however, some states operating their own OSHA approved job safety and health programs will continue to enforce the 100 .mu.g/m.sup.3 standard. NIOSH has set its Recommended Exposure Limits (REL) at 50 .mu.g/m.sup.3. These values are 8-hr time-weighted averages.
The OSHA PELs are required to consider the feasibility of controlling exposures in various industries where the agents are used; the NIOSH PELs, by contrast, are based primarily on concerns relating to the prevention of occupational disease. The American Conference of Governmental Industrial Hygienist (ACGTH) has set the Threshold Limit Value (TLV) for crystalline quartz silica at 100 .mu.g/m.sup.3, 8-hr time-weighted averages. All of these exposure limits (PEL, REL, TLV) are for the respirable fraction of the silica containing dust.
One ventilated hand grinding bench currently used for cleaning foundry castings is described in a publication entitled "Industrial Ventilation: A Manual of Recommended Practice 21st Ed." (American Conference of Governmental Industrial Hygienists (ACGIH), 1992). The present inventors have discovered that while a ventilation work bench can reduce silica exposure, tool usage and work practices nevertheless can have an adverse effect on the worker's silica exposure.
The present invention provides for a device which can avoid adverse effects of tool usage and work practices which influence silica exposure.